A theoretical capacity of a lithium sulfur secondary battery including sulfur as a cathode material, which is 1672 mAh/g, is very high, and is ten times a theoretical capacity of a lithium secondary battery including LiCoO2 or the like as a prevailing cathode active material, which is 137 mAh/g. Further, sulfur is low in cost and is abundant as a resource.
Japanese Patent Application Laid-Open Publication No. 2013-229227 discloses a method of reducing lithium sulfate by heating a mixture of lithium sulfate particles and carbon particles at 830° C. and producing a cathode material composed of carbon particles and lithium sulfide particles.
However, it is not easy to perform the heating at a high temperature while fine particles containing lithium sulfate and carbon fine particles are uniformly mixed.